WO2013145768A1

WO2013145768A1 - Cylindrical battery

Info

Publication number: WO2013145768A1
Application number: PCT/JP2013/002151
Authority: WO
Inventors: 柿沼　彰; 慧介米田; 増本　兼人
Original assignee: パナソニック株式会社
Priority date: 2012-03-30
Filing date: 2013-03-29
Publication date: 2013-10-03
Also published as: CN103797607B; EP2752913B1; EP2752913A1; JPWO2013145768A1; CN103797607A; JP5512057B2; US20140242448A1; KR20140046081A; EP2752913A4; KR101476963B1; US9231234B2

Abstract

Provided is a compact cylindrical battery which achieves both the improvement of battery characteristics and the improvement of long-term reliability and safety. A cylindrical battery is provided with: a closed-end cylindrical battery case (1); an electrode group (5) housed, together with an electrolyte, in the battery case (1); a sealing member (8) fitted in an opening of the battery case (1); and a gasket (9) interposed between the sealing member (8) and the battery case (1), and the opening of the battery case (1) is sealed by drawing an open end of the battery case (1). The battery case (1) is produced from stainless steel. Further, the outer diameter of the battery case (1) is 10 mm or less, and the thickness of the battery case (1) is 0.05-0.2 mm inclusive.

Description

Cylindrical battery

The present invention relates to a cylindrical battery equipped with a battery case, such as a lithium ion secondary battery.

In recent years, lithium ion secondary batteries have been widely used as power sources for driving electronic devices such as portable digital devices. In particular, in a portable device such as a smartphone that requires a heavy load with multiple functions, an improvement in battery characteristics such as energy density and load characteristics and a reduction in weight are required for a battery used as a power source. Furthermore, improvement in long-term reliability and safety is required.

A lithium ion secondary battery usually includes a metal battery case. The thickness of the battery case is reduced to increase the internal volume, and the battery case is filled with power generation elements at a high density. The density can be improved. Reducing the thickness of the battery case is particularly effective for a small battery in that the internal volume is increased. As another example, there is a lithium ion battery using a metal-resin laminate sheet instead of the battery case. In this case, this thin sheet encloses battery components such as positive and negative electrodes, a separator, and an electrolytic solution, thereby realizing improvement in energy density and weight reduction.

JP 2009-181754 A JP 2008-223087 A JP 2007-227339 A

However, in batteries such as lithium ion secondary batteries, it has been difficult to achieve both improved battery characteristics and improved long-term reliability and safety. For example, in a lithium ion secondary battery, iron, aluminum, or the like is generally used as a battery case material. For this reason, if the thickness of the metal plate which comprises a battery case is made small for the improvement of an energy density, the intensity | strength of a battery case will fall. A decrease in the strength of the battery case results in a decrease in sealing performance and a decrease in tolerance for an increase in internal pressure caused by gas plate expansion and gas caused by repeated charge / discharge cycles. As a result, deformation of the battery case and deterioration of battery characteristics are likely to occur, and it becomes difficult to achieve long-term reliability.

In addition, when a metal-resin laminate sheet is used instead of the battery case, although the energy density is improved, a problem caused by a decrease in the strength of the battery case becomes obvious. For example, simply by repeating a normal charge / discharge cycle, gas is generated by the decomposition of the electrolyte, which increases the internal pressure and significantly expands the battery. Further, since the sealing performance in the vicinity of the lead portion is fragile, moisture easily enters from the outside to the inside of the battery. For this reason, gas is generated due to the moisture, thereby increasing the internal pressure and expanding the battery. These expansions may destroy the sealing by the laminate sheet.

In this way, to improve battery characteristics and improve long-term reliability and safety, a battery case is used, and the battery case achieves high strength and high sealing performance while reducing its thickness. It is very important to do.

Therefore, the strength of the opening of the battery case is increased by increasing only the thickness of the opening of the battery case so that high sealing performance can be obtained when the opening of the battery case is caulked. A technique has been proposed (see, for example, Patent Document 1). However, such a battery case is not suitable for mass production because it has a complicated shape and is difficult to mold and control quality.

In addition, a technique has been proposed in which an aluminum alloy material whose strength is increased by the addition of a different metal and a heat treatment is used as a battery case material (see, for example, Patent Document 2). However, simply increasing the strength of the battery case reduces the workability of the battery case and makes it difficult to achieve high sealing performance.

Therefore, an object of the present invention is to provide a small cylindrical battery in which both improvement in battery characteristics and improvement in long-term reliability and safety are realized.

The inventors of the present invention have made intensive efforts to find a condition in which improvement in battery characteristics and improvement in long-term reliability and safety can be achieved in a small cylindrical battery.

A cylindrical battery according to the present invention includes a bottomed cylindrical battery case, an electrode group housed in the battery case together with an electrolyte, a sealing member fitted in an opening of the battery case, a sealing member, and the battery case. An opening portion of the battery case is sealed by drawing the opening end portion of the battery case. The battery case is made of stainless steel. Further, the outer diameter of the battery case is 10 mm or less, and the thickness of the battery case is 0.05 mm or more and 0.2 mm or less.

The cylindrical battery according to the present invention achieves both improved battery characteristics and improved long-term reliability and safety.

The novel features of the invention are set forth in the appended claims, and the invention will be described both in terms of structure and content, together with other objects and features of the invention, and by the following detailed description in conjunction with the drawings. It will be better understood.

1 is a longitudinal sectional view conceptually showing a cylindrical battery according to an embodiment of the present invention.

First, the cylindrical battery according to the present invention will be described.
A cylindrical battery according to the present invention includes a bottomed cylindrical battery case, an electrode group housed in the battery case together with an electrolyte, a sealing member fitted in an opening of the battery case, a sealing member, and the battery case. An opening portion of the battery case is sealed by drawing the opening end portion of the battery case. The battery case is made of stainless steel. The outer diameter of the battery case is 10 mm or less, and the thickness of the battery case is 0.05 mm or more and 0.2 mm or less.

As shown in Table 1, stainless steel has a significantly higher tensile fracture strength than iron (Fe) and aluminum (Al). In Table 1, SUS316L (austenitic stainless steel) is listed as an example of stainless steel. Therefore, by using stainless steel as the material of the battery case as in the present invention, high strength is maintained in the battery case even when the thickness of the battery case is reduced as a whole in a uniform state. Stainless steel is excellent in workability despite its high strength. Therefore, high sealing performance is realized in the battery case.

The inventors of the present invention have a high sealing performance in a small cylindrical battery whose outer diameter is 10 mm or less, particularly when the thickness of the battery case is 0.05 mm or more and 0.2 mm or less. I found out that it would be realized. In addition, the present inventors have found that these conditions are particularly preferable for a small cylindrical battery whose outer diameter is 6 mm or less. Thus, in a small cylindrical battery, when sealing the opening of the battery case by drawing the opening end of the battery case, the thickness of the battery case is a condition for enhancing the sealing property. Very important.

When the drawing process is performed on the opening end of the battery case, the battery case contracts in the squeezed portion of the battery case (that is, the diameter of the battery case is reduced). When the diameter of the battery case before the drawing process is 15 mm or more, the shrinkage change rate of the battery case 1 by the drawing process is small and hardly affects the sealing performance. However, when the diameter of the battery case 1 before the drawing process is 10 mm or less, the shrinkage change rate of the battery case 1 due to the drawing process becomes large, and the roundness is reduced or the wrinkles are abnormal at the opening end of the battery case. Deformation easily occurs. Such a problem is conspicuous when the diameter of the battery case before drawing is 6 mm or less, which lowers the sealing performance. In this way, in a small cylindrical battery having a large shrinkage change rate of the battery case 1 due to drawing, the inventors have made the battery case 1 made of stainless steel and the thickness of the battery case 1 is 0.05 mm. It has been found that high sealing performance is realized when the thickness is 0.2 mm or less.

When the cylindrical battery is a lithium ion battery, the battery case is preferably made of a material having a wide potential window and high acid corrosion resistance. In this respect, stainless steel such as SUS316L is very strong with respect to the potential on the reduction side, and has a wider potential window on the oxidation side than iron or copper, though not as much as aluminum. In addition, when a reduction potential is applied to aluminum in the presence of lithium ions, lithium is deposited on the surface to form an alloy with lithium. Since such an alloying reaction involves volume expansion, when the battery case is made of aluminum, the battery case becomes brittle and its strength decreases, and therefore it is difficult to achieve long-term reliability of the battery. is there.

Stainless steel has higher acid corrosion resistance than iron, copper and aluminum. This is because stainless steel has a protective layer on its surface. In lithium ion batteries, lithium hexafluorophosphate (LiPF ₆ ) is generally used as a supporting electrolyte. Such a supporting electrolyte constitutes an electrolytic solution having high ionic conductivity and can realize excellent load characteristics. On the other hand, lithium hexafluorophosphate hydrolyzes in the presence of moisture to generate hydrofluoric acid (HF), which is a strong acid. Therefore, in lithium-ion batteries, in addition to suppressing the entry of moisture from the outside by enhancing the sealing performance, it is important to improve the acid corrosion resistance of the battery case in order to achieve long-term reliability. is there. This is because the corrosion of the battery case causes intrusion of moisture and accelerates the progress of the corrosion.

Thus, according to the cylindrical battery according to the present invention, it is possible to achieve both the improvement of battery characteristics and the improvement of long-term reliability and safety. In addition, since the thickness of the battery case can be made uniform, the battery case can be easily molded and quality controlled.

In a preferable specific configuration of the cylindrical battery, the stainless steel constituting the battery case is an austenitic stainless steel having a low carbon content. The stainless steel constituting the battery case is preferably stainless steel having a carbon content of 0.08% by mass or less. Furthermore, the carbon content in the stainless steel is more preferably 0.05% by mass or less, and particularly preferably 0.03% by mass or less.

As shown in Table 1, the stainless steel with such a low carbon content has a high elongation and a high tensile strength at break. Therefore, stainless steel with a low carbon content has high workability. That is, when forming the battery case 1, it is easy to stretch and thin the stainless steel, and the processing accuracy is high. For example, in an elongated cylindrical battery, a battery case having a large ratio of height to diameter can be easily formed with high accuracy by, for example, deep drawing. Therefore, the battery case 1 having a thickness of 0.05 mm or more and 0.2 mm or less can be formed easily and with high accuracy, and as a result, a cylindrical battery having high sealing performance is stably manufactured. It becomes possible.

In another preferable specific configuration of the cylindrical battery, the stainless steel constituting the battery case 1 is stainless steel having a copper content of 1.0% by mass or more and 6.0% by mass or less. More preferably, copper content is 1.5 mass% or more and 5.0 mass% or less. Thus, the stainless steel containing copper has high tensile fracture strength, elongation rate, and acid corrosion resistance, and has low contact resistance on the stainless steel surface as shown in Table 2. In addition, the protective layer which raises acid corrosion resistance is normally formed in the surface of stainless steel, and when stainless steel does not contain copper, this protective layer becomes a cause which enlarges contact resistance. On the other hand, when stainless steel contains copper, the resistance of the protective layer is reduced, and as a result, the contact resistance is reduced.

According to stainless steel containing copper, it is possible to easily obtain electrical contact with equipment without forming a new surface layer or terminal. Further, by increasing the contact area with the electrode inside the battery, the internal resistance of the battery is reduced without joining the battery case and the electrode by welding or the like, and as a result, good load characteristics can be obtained.

As described above, stainless steel has high strength. Therefore, a large force is required when processing stainless steel into a desired shape. Accordingly, the battery case is preferably formed by deep drawing a stainless steel plate having a small thickness to form a bottomed cylinder. According to deep drawing, it is possible to obtain a battery case having a small and uniform thickness and a small variation in shape and thickness. Also, deep drawing reduces material loss. Therefore, in the cylindrical battery, it is possible to achieve both improvement in battery characteristics and improvement in long-term reliability and safety.

As methods for processing stainless steel into a bottomed cylindrical shape, there are methods such as an impact press method and a DI (Drawing & Ironing) method. However, in these methods, it is necessary to apply a large force evenly during the processing and molding, and it is difficult to control the shape. Therefore, the shape and thickness of the battery case are likely to vary. In particular, when the thickness of the battery case is reduced, holes are formed or fractured. In addition, as a method for processing stainless steel into a bottomed cylindrical shape, there is a method of cutting a columnar material. However, with this method, although it is difficult for variations in the shape of the battery case to occur, material loss is large and it is not efficient.

Next, embodiments of the present invention will be specifically described with reference to the drawings. In addition, each part structure of this invention is not restricted to embodiment, A various deformation | transformation is possible within the technical scope as described in a claim.
FIG. 1 is a longitudinal sectional view conceptually showing a cylindrical battery according to an embodiment of the present invention. As shown in FIG. 1, a cylindrical battery includes a bottomed cylindrical battery case 1, an electrode group 5 housed in the battery case 1 together with a nonaqueous electrolyte, and a sealing member fitted in the opening of the battery case 1. 8 and a gasket 9 interposed between the sealing member 8 and the battery case 1.

≪Battery case≫
The battery case 1 is formed by deep drawing a stainless steel material having a uniform thickness. The outer diameter of the battery case 1 is 10 mm or less, and particularly preferably 6 mm or less. The thickness of the battery case 1 is 0.05 mm or more and 0.2 mm or less. The ratio of the side wall thickness (side thickness) to the bottom thickness (bottom thickness) of the battery case 1 is 0.20 or more and 1.20 or less, preferably 0.33 or more and 1.05 or less. is there.

The stainless steel constituting the battery case 1 is preferably an austenitic stainless steel having a low carbon content. The stainless steel constituting the battery case 1 is preferably stainless steel having a carbon content of 0.08% by mass or less. Furthermore, the carbon content in the stainless steel is more preferably 0.05% by mass or less, and particularly preferably 0.03% by mass or less.

The stainless steel constituting the battery case 1 preferably contains copper. In such a battery case 1, the content of copper is preferably 1.0% by mass or more and 6.0% by mass or less, and particularly preferably 1.5% by mass or more and 5.0% by mass or less. .

≪Sealing member and gasket≫
The sealing member 8 and the gasket 9 are members that seal the opening of the battery case 1. Specifically, the sealing member 8 and the gasket 9 are inserted into the opening of the battery case 1 such that the gasket 9 is interposed between the sealing member 8 and the battery case 1. The opening end of the battery case 1 is drawn, and the opening end is caulked to the sealing member 8. Therefore, the gasket 9 is in close contact with the side surface of the sealing member 8 and the inner surface of the battery case 1 in a compressed state. In this way, the opening of the battery case 1 is sealed. Further, a perforated disk 11 made of an electrical insulating material is fitted into a protruding portion of the sealing member 8 exposed to the outside of the battery case 1. The disk 11 prevents an electrical short circuit between the sealing member 8 and the battery case 1.

The gasket 9 is made of polypropylene (PP), polyethylene (PE), polyphenylene sulfide (PPS), perfluoroalkylethylene-hexafluoropropylene copolymer (PFA), cross-linked rubber, or the like. In particular, PFA is preferable because it has low moisture permeability and can suppress the ingress of moisture into the battery, which can cause deterioration of the lithium ion battery.

≪Electrode group≫
The electrode group 5 includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4. In the electrode group 5, the negative electrode plate 2 and the positive electrode plate 3 are overlapped with each other and wound with the separator 4 interposed therebetween. The winding end portion of at least one of the negative electrode plate 2 and the positive electrode plate 3 is fixed to the outer peripheral surface of the electrode group 5 with a fixing tape so that the electrode group 5 is not displaced. The electrode group 5 is housed in the battery case 1 together with a non-aqueous electrolyte (not shown). According to such an electrode group 5, the reaction area becomes large, and it is possible to realize a heavy load characteristic.

As will be described later, each of the negative electrode plate 2 and the positive electrode plate 3 is composed of a core material that is a current collector and a mixture layer (including an active material) formed on the surface of the core material. And in order to increase battery capacity, the mixture layer is formed in the surface of the core material in the compressed state. For this reason, in the electrode group 5, if the radius at the beginning of winding of the negative electrode plate 2 and the positive electrode plate 3 is too small, the mixture layer peels off from the core material, and this causes electrical damage in the battery case 1. There is a risk of a short circuit (internal short circuit). On the other hand, when the winding start radius is too large, the amount of the active material stored in the battery case 1 is reduced, and the battery capacity is reduced. Therefore, it is necessary to start winding the negative electrode plate 2 and the positive electrode plate 3 with an appropriate radius. For example, when winding the negative electrode plate 2 and the positive electrode plate 3 using a winding core, the diameter R of the winding core is preferably 0.6 mm or more and 3.0 mm or less, and 0.8 mm or more and less than 1.5 mm. It is particularly preferred. In the vicinity of the central axis of the electrode group 5, there is a space where no active material is present. The space preferably has a diameter of 3.0 mm or less, and particularly preferably has a diameter of less than 1.5 mm. .

A negative electrode lead 6 is electrically connected to the negative electrode plate 2 (specifically, a negative electrode core material to be described later), and the end of the negative electrode lead 6 is joined to the inner surface of the side wall of the battery case 1 by spot welding or the like. Has been. When the stainless steel constituting the battery case 1 contains copper, the negative electrode lead 6 may be simply brought into contact with the inner surface of the side wall of the battery case 1. Thus, the negative electrode plate 2 is electrically connected to the battery case 1, and the battery case 1 functions as a negative electrode terminal. For example, nickel, iron, stainless steel, copper, or the like is used for the negative electrode lead 6. The negative electrode lead 6 has a characteristic of being bent by a small pressure, and the shape thereof is not particularly limited, but a strip having a margin for welding with the negative electrode core and a margin for welding with the battery case 1. Examples thereof include an ellipse or a polygon inscribed in the shape and the strip shape. Further, the thickness of the negative electrode lead 6 is preferably 10 μm or more and 120 μm or less, and particularly preferably 20 μm or more and 80 μm or less.

A positive electrode lead 7 is electrically connected to the positive electrode plate 3 (specifically, a positive electrode core material to be described later), and an end of the positive electrode lead 7 is joined to the sealing member 8 by spot welding or the like. . Thus, the positive electrode plate 3 is electrically connected to the sealing member 8, and the sealing member 8 functions as a positive electrode terminal. As the material of the positive electrode lead 7, for example, aluminum is used. The positive electrode lead 7 has a characteristic of being bent with a small pressure, and the shape thereof is not particularly limited, but examples thereof include a strip shape. The thickness of the positive electrode lead 7 is preferably 40 μm or more and 150 μm or less, and particularly preferably 50 μm or more and 100 μm or less.

A ring-shaped intermediate member 10 made of an electrical insulating material is disposed between the electrode group 5 and the sealing member 8, and the positive electrode lead 7 passes through the inner side of the intermediate member 10 and the positive electrode plate 3. It is connected to the sealing member 8. Thereby, the intermediate member 10 prevents an electrical short circuit between the negative electrode and the positive electrode.

<Negative electrode plate>
The negative electrode plate 2 includes a negative electrode core material that is a negative electrode current collector, and a negative electrode mixture layer formed on the surface of the negative electrode core material. The negative electrode plate 2 is formed, for example, by depositing a negative electrode active material in a thin film on the surface of the negative electrode core material. The negative electrode core material is a metal foil. For the negative electrode core material, for example, a long conductive substrate having a porous structure or a nonporous structure is used. As a material for the negative electrode core material, for example, stainless steel, nickel, copper, or the like is used. The thickness of the negative electrode core material is not particularly limited, but is preferably 1 μm or more and 500 μm or less, and particularly preferably 5 μm or more and 20 μm or less. According to the negative electrode core material having such a thickness, the negative electrode plate 2 can be reduced in weight while maintaining the strength of the negative electrode plate 2.

The negative electrode mixture layer contains a negative electrode active material. Therefore, the negative electrode active material will be described in detail below. The negative electrode mixture layer preferably contains a binder or the like in addition to the negative electrode active material.
(Negative electrode active material)
As the negative electrode active material, a material capable of occluding and releasing lithium ions is used. Examples of such a negative electrode active material include metals, metal fibers, carbon materials, oxides, nitrides, silicon compounds, tin compounds, and various alloy materials. Specific examples of the carbon material include, for example, various natural graphites, cokes, graphitized carbon, carbon fibers, spherical carbon, various artificial graphites, and amorphous carbon.

Here, a simple substance such as silicon (Si) or tin (Sn), or a silicon compound or tin compound has a large capacity density. For this reason, it is preferable to use silicon, tin, a silicon compound, or a tin compound as the negative electrode active material. Specific examples of the silicon compound include, for example, SiOx (where 0.05 <x <1.95), or B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, Examples thereof include a silicon alloy in which a part of Si is substituted with at least one element selected from the group consisting of V, W, Zn, C, N, and Sn, or a silicon solid solution. Specific examples of the tin compound include Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (where 0 <x <2), SnO ₂ , SnSiO _{3 and the} like. In addition, a negative electrode active material may be used individually by 1 type among the negative electrode active materials enumerated above, and may be used in combination of 2 or more type.

<Positive electrode plate>
The positive electrode plate 3 includes a positive electrode core material that is a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode core material. The positive electrode core material is a metal foil. For the positive electrode core material, for example, a long conductive substrate having a porous structure or a nonporous structure is used. As the material for the positive electrode core material, for example, aluminum or the like is used. The thickness of the positive electrode core material is not particularly limited, but is preferably 8 μm or more and 25 μm or less, and particularly preferably 10 μm or more and 15 μm or less. According to the positive electrode core material having such a thickness, it is possible to configure the electrode group 5 that is smoothly curved and has a small diameter.

The positive electrode mixture layer includes a positive electrode active material, a binder, and a conductive agent. Therefore, the positive electrode active material, the binder, and the conductive agent will be described in detail below.
(Positive electrode active material)
As the positive electrode active material, a lithium-containing composite oxide is preferable. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiCo _x Ni _1-x O ₂ , LiCo _x M _1-x O ₂ , LiNi _x M _1-x O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiMnMO ₄ , LiMePO ₄ , Li ₂ MePO ₄ F (where M is Na, Mg, Sc, Y, Mn, Fe, Co , Ni, Cu, Zn, Al, Cr, Pb, Sb and B. x is 0 <x <1, Me is at least selected from Fe, Mn, Co, Ni In addition, one of these lithium-containing compounds may be substituted with a different element. Further, as the positive electrode active material, a positive electrode active material surface-treated with a metal oxide, a lithium oxide, a conductive agent, or the like may be used. Examples of the surface treatment include a hydrophobic treatment.

The average particle diameter of the positive electrode active material is preferably 5 μm or more and 20 μm or less. When the average particle diameter of the positive electrode active material is less than 5 μm, the surface area of the active material particles becomes extremely large. For this reason, the amount of the binder for obtaining the adhesive strength that enables handling of the positive electrode plate 3 is extremely increased. For this reason, the amount of active material per electrode plate is reduced, and the capacity is reduced. On the other hand, when the thickness exceeds 20 μm, coating stripes are likely to occur when the positive electrode mixture slurry is applied to the positive electrode core material.

(Binder)
As binders, for example, PVDF, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, polyacrylic acid ethyl ester, polyacrylic Acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene butadiene rubber or carboxy Examples include methyl cellulose. Or two kinds selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid and hexadiene Examples thereof include a copolymer obtained by copolymerizing the above materials, or a mixture obtained by mixing two or more selected materials.

Among the binders listed above, in particular, PVDF and derivatives thereof are chemically stable in the non-aqueous electrolyte secondary battery, and sufficiently bind the positive electrode mixture layer and the positive electrode core material, Since the positive electrode active material constituting the positive electrode mixture layer, the binder, and the conductive agent are sufficiently bound, good charge / discharge cycle characteristics and discharge performance can be obtained. Therefore, it is preferable to use PVDF or a derivative thereof as the binder of this embodiment. In addition, PVDF and its derivatives are preferable in terms of cost because they are inexpensive. In order to prepare a positive electrode using PVDF as a binder, for example, when PVDF is dissolved in N-methylpyrrolidone and used, or powdered PVDF is dissolved in a positive electrode mixture slurry. The case where it is made to use is mentioned.

(Conductive agent)
Examples of the conductive agent include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black (AB), ketjen black, channel black, furnace black, lamp black or thermal black, carbon fiber or metal. Conductive fibers such as fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, or organic conductivity such as phenylene derivatives Materials and the like.

<Separator>
For the separator 4, a microporous thin film, a woven fabric, a non-woven fabric, or the like having high ion permeability and having a predetermined mechanical strength and electrical insulation is used. In particular, it is preferable to use a polyolefin such as polypropylene or polyethylene as the material for the separator 4. Since polyolefin has excellent durability and a shutdown function, the safety of the lithium ion secondary battery can be improved.

The thickness of the separator 4 is generally 10 μm or more and 300 μm or less, and preferably 10 μm or more and 40 μm or less. Further, the thickness of the separator 4 is more preferably 15 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. When a microporous thin film is used as the separator 4, the microporous thin film may be a single layer film made of one kind of material, or a composite film or multilayer film made of one kind or two or more kinds of materials. There may be. Further, the porosity of the separator 4 is preferably 30% or more and 70% or less, and particularly preferably 35% or more and 60% or less. Here, the porosity indicates the ratio of the volume of the entire hole to the total volume of the separator 4.

<Nonaqueous electrolyte>
As the non-aqueous electrolyte stored in the battery case 1, a liquid, gel-like, or solid non-aqueous electrolyte can be used. The liquid non-aqueous electrolyte contains an electrolyte salt (for example, lithium salt) and a non-aqueous solvent in which the electrolyte salt is dissolved. The gel-like non-aqueous electrolyte includes a non-aqueous electrolyte and a polymer material that holds the non-aqueous electrolyte. Examples of the polymer material include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, and polyvinylidene fluoride hexafluoropropylene. The solid non-aqueous electrolyte includes a polymer solid electrolyte.

The nonaqueous solvent and electrolyte salt contained in the liquid nonaqueous electrolyte will be described in detail below.

(Non-aqueous solvent)
As the non-aqueous solvent for dissolving the electrolyte salt, a known non-aqueous solvent can be used. Although the kind of this non-aqueous solvent is not specifically limited, For example, cyclic carbonate ester, chain | strand-shaped carbonate ester, or cyclic carboxylic acid ester etc. are used. Here, specific examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Specific examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and the like. Specific examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). As the non-aqueous solvent, one of the non-aqueous solvents listed above may be used alone, or two or more thereof may be used in combination.

(Electrolyte salt)
Examples of the electrolyte salt dissolved in the non-aqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , and lower aliphatic. Lithium carboxylate, LiCl, LiBr, LiI, chloroborane lithium, borates, imide salts and the like are used. Here, specific examples of borates include, for example, bis (1,2-benzenediolate (2-)-O, O ′) lithium borate, bis (2,3-naphthalenedioleate (2-)-O , O ′) lithium borate, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, or bis (5-fluoro-2-olate-1-benzenesulfonic acid-O , O ′) lithium borate and the like. As specific examples of imide salts, for example, lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO _2)), or the like bispentafluoroethanesulfonyl imide lithium _{_{_{_{((C 2 F 5 SO 2}}}} ) 2 NLi) and the like. As the electrolyte salt, one of the electrolyte salts listed above may be used alone, or two or more thereof may be used in combination.

The amount of the electrolyte salt dissolved in the non-aqueous solvent is preferably 0.5 mol / m ³ or more and 2 mol / m ³ or less.

In addition to the electrolyte salt and the nonaqueous solvent, the liquid nonaqueous electrolyte may contain an additive that decomposes on, for example, the negative electrode to form a film having high lithium ion conductivity and increases the charge / discharge efficiency of the battery. Examples of additives having such a function include vinylene carbonate (VC), 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4-ethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, 4 -Propyl vinylene carbonate, 4,5-dipropyl vinylene carbonate, 4-phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl ethylene carbonate (VEC), divinyl ethylene carbonate, and the like. An additive may be used individually by 1 type among the additives enumerated above, and may be used in combination of 2 or more type. In particular, among the additives listed above, at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate is preferable. The additive may be one in which some of the hydrogen atoms of the additives listed above are substituted with fluorine atoms.

Furthermore, the liquid non-aqueous electrolyte may contain, in addition to the electrolyte salt and the non-aqueous solvent, for example, a known benzene derivative that decomposes during overcharge to form a film on the electrode and inactivate the battery. As the benzene derivative having such a function, those having a phenyl group and a cyclic compound group adjacent to the phenyl group are preferable. Here, specific examples of the benzene derivative include, for example, cyclohexylbenzene, biphenyl, diphenyl ether, and the like. Specific examples of the cyclic compound group contained in the benzene derivative include, for example, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, or a phenoxy group. A benzene derivative may be used individually by 1 type among the benzene derivatives enumerated above, and may be used in combination of 2 or more type. However, the content of the benzene derivative with respect to the non-aqueous solvent is preferably 10 vol% or less of the entire non-aqueous solvent.

Examples of the present invention will be specifically described below.
<Example 1>
(Preparation of positive electrode plate)
As the positive electrode active material, LiNi _0.82 Co _0.15 Al _0.03 O ₂ having an average particle diameter of 10 μm was prepared. As a binder, 4.7 vol% PVDF was prepared with respect to 100 vol% of the positive electrode active material. As a conductive agent, 4.5 vol% acetylene black was prepared with respect to 100 vol% of the positive electrode active material. Further, N-methylpyrrolidone (NMP) was prepared as a solvent, and the prepared binder was dissolved in this solvent to prepare a solution. And the positive electrode mixture slurry was prepared by mixing the prepared positive electrode active material, the electrically conductive agent, and the solution.

Next, an aluminum foil having a thickness of 15 μm was prepared as a positive electrode core material, a positive electrode mixture slurry was applied to both surfaces of the aluminum foil, and then dried. Thereafter, the positive electrode core material coated with the positive electrode mixture slurry on both sides and dried was rolled to produce a plate-shaped positive electrode plate having a thickness of 0.12 mm. The positive electrode plate 3 having a thickness of 0.12 mm, a width of 30.5 mm, and a length of 19.0 mm was produced by cutting the positive electrode plate into a width of 30.5 mm and a length of 19.0 mm.

(Preparation of negative electrode plate)
As the negative electrode active material, scaly graphite having an average particle size of 20 μm was prepared. As a binder, 4.7 vol% SBR was prepared with respect to 100 vol% of the negative electrode active material. As a conductive agent, 4.5 vol% acetylene black was prepared with respect to 100 vol% of the negative electrode active material. Also, pure water was prepared as a solvent, and the prepared binder was dissolved in this solvent to prepare a solution. And the negative mix slurry was prepared by mixing the prepared negative electrode active material, the electrically conductive agent, and a solution.

Next, a copper foil having a thickness of 8 μm was prepared as a negative electrode core material, a negative electrode mixture slurry was applied to both surfaces of the copper foil, and then dried. Thereafter, the negative electrode core material coated with the negative electrode mixture slurry on both sides and dried was rolled to produce a plate-shaped negative electrode plate having a thickness of 0.15 mm. Then, the negative electrode plate 2 having a thickness of 0.15 mm, a width of 29.5 mm, and a length of 37.0 mm was produced by cutting the negative electrode plate into a width of 29.5 mm and a length of 37.0 mm.

(Preparation of non-aqueous electrolyte)
As a non-aqueous solvent, a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed so that the volume ratio was 1: 3 was prepared. LiPF ₆ was prepared as an electrolyte salt. Then, 5 wt% vinylene carbonate is added to the prepared nonaqueous solvent as an additive for increasing the charge / discharge efficiency of the battery, and the electrolyte salt is such that the molar concentration with respect to the nonaqueous solvent is 1.4 mol / m ^3. LiPF ₆ was dissolved, thereby preparing a nonaqueous electrolyte.

(Production of cylindrical battery)
First, the positive electrode lead 7 made of aluminum was attached to the positive electrode core material of the prepared positive electrode plate 3, and the negative electrode lead 6 made of nickel was attached to the negative electrode core material of the prepared negative electrode plate 2. Thereafter, the negative electrode plate 2 and the positive electrode plate 3 were wound in a state where a polyethylene separator 4 (thickness: 16 μm) was interposed between them, thereby producing an electrode group 5. Further, a battery case 1 having a thickness of 0.1 mm and an outer diameter of 3.5 mm using SUS316L (austenitic stainless steel having no copper content and a carbon content of 0.03% by mass or less). Was made.

Next, the intermediate member 10 was disposed on the upper end of the electrode group 5. The negative electrode lead 6 was welded to the battery case 1 and the positive electrode lead 7 was welded to the sealing member 8. The electrode group 5 was housed in the battery case 1. Thereafter, a nonaqueous electrolyte was injected into the battery case 1 by a decompression method. Thereafter, a gasket 9 made of a sealing member 8 and PFA was inserted into the opening of the battery case 1 so that the gasket 9 was interposed between the battery case 1 and the sealing member 8. And the cylindrical battery of diameter 3.5mm and height 35mm was produced by crimping the opening edge part of the battery case 1 to the sealing member 8. FIG. This cylindrical battery was referred to as Example 1.

<Example 2>
As the stainless steel constituting the battery case 1, an austenitic stainless steel having a copper content of 3.80% by mass was used. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Example 2.

<Example 3>
SUS316L was used as a material constituting the battery case 1, and the thickness of the battery case 1 (outer diameter 3.5 mm) was 0.15 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Example 3.

<Example 4>
SUS316L was used as the material constituting the battery case 1, and the thickness of the battery case 1 (outer diameter 3.5 mm) was 0.20 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Example 4.

<Comparative Example 1>
SUS316L was used as a material constituting the battery case 1, and the thickness of the battery case 1 (outer diameter 3.5 mm) was 0.25 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 1.

<Comparative example 2>
Iron (Fe) was used as a material constituting the battery case 1 (thickness 0.1 mm, outer diameter 3.5 mm). Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 2.

<Comparative Example 3>
Iron (Fe) was used as a material constituting the battery case 1, and the thickness of the battery case 1 (outer diameter 3.5 mm) was 0.2 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 3.

The cylindrical batteries of Examples 1 to 4 and the cylindrical batteries of Comparative Examples 1 to 3 were each manufactured in five pieces, and for these cylindrical batteries, the average value of the energy density, the rate of occurrence of liquid leakage, and the internal short circuit The incidence was determined. These results are shown in Table 3. The internal short-circuit occurrence rate is a short-circuit occurrence rate when a tip of a round bar having a diameter of 1.0 mm is pressed against the side surface of the cylindrical battery and a stress of 1.5 kgf is applied in this state.

The long-term reliability test was further performed on the cylindrical batteries of Examples 1 to 4 and the cylindrical batteries of Comparative Examples 1 to 3. Specifically, these cylindrical batteries were stored in an atmosphere of 85 ° C.-90% RH for 20 days, and then the expansion rate of the battery case 1 and the maintenance rate of the battery capacity were determined. In addition, the rate of increase in the outer diameter of the battery case 1 was determined as the expansion rate of the battery case 1. The battery capacity retention rate was determined based on the initial battery capacity. These results are shown in Table 4.

By comparing Examples 1 to 4 and Comparative Example 1 in Table 3, the energy density is small in Comparative Example 1 where the thickness of the battery case 1 is large, and the energy density decreases as the thickness of the battery case 1 decreases. It turns out that it grows. This is because as the thickness of the battery case 1 decreases, the internal volume of the battery case 1 (which stores the power generation element) increases.

By comparing Example 1 and Comparative Example 2 in Tables 3 and 4, the following differences were observed even though the thickness of the battery case 1 was the same 0.10 mm. That is, in Comparative Example 2 in which the material of the battery case 1 is iron, an internal short circuit is likely to occur and the battery case 1 is easily expanded, whereas in Example 1 in which the material of the battery case 1 is SUS316L, An internal short circuit did not occur and the battery case 1 did not expand. This is because the strength of SUS316L is higher than the strength of iron (Fe), and thus the strength of the battery case 1 made of SUS316L is increased. The expansion of the battery case 1 in Comparative Example 2 is considered to be due to the generation of hydrogen gas due to the influence of moisture that has entered the battery case.

By comparing Examples 1 to 4 and Comparative Example 1 in Table 3, the thickness of the battery case 1 despite the fact that the material of the battery case 1 is the same SUS316L and the outer diameter is the same 3.5 mm. In Comparative Example 1 in which the thickness is 0.25 mm, liquid leakage is likely to occur, whereas in Examples 1 to 4 in which the thickness is 0.20 mm or less, liquid leakage does not occur. That is, it was found that high sealing performance was achieved in Examples 1 to 4. This is because in Examples 1 to 4, there is no occurrence of an abnormal shape such as a decrease in roundness or wrinkles, and therefore a path that causes liquid leakage is not formed.

By comparing Examples 1 to 4 and Comparative Example 1 in Table 4, in Comparative Example 1 where the thickness of the battery case 1 is 0.25 mm even though the material of the battery case 1 is the same SUS316L. It was found that, while the capacity retention rate was remarkably lowered, in Examples 1 to 4 whose thickness was 0.20 mm or less, the capacity retention rate was increased to 50% or more. This is because in Examples 1 to 4, there is no occurrence of an abnormal shape such as a decrease in roundness or wrinkles, and therefore, evaporation of the electrolyte and entry of moisture from the outside are suppressed.

On the other hand, in Comparative Examples 2 and 3 in which the material of the battery case 1 was iron (Fe), the capacity retention rate was remarkably low. This is because the strength of the battery case 1 is low, so that the battery case 1 easily expands with the generation of hydrogen gas. Therefore, the sealing property (see the liquid leakage occurrence rate in Table 3) is lowered and the battery characteristics are deteriorated. Because. In addition, it is thought that the battery case corroded due to the generation of hydrofluoric acid, which is a strong acid, and the corrosion caused the invasion of moisture and accelerated the progress of corrosion, so that it was impossible to maintain a high battery capacity. It is done.

By comparing Example 1 and Example 2 in Tables 3 and 4, even if the stainless steel constituting the battery case 1 contains copper, the copper adversely affects battery characteristics and long-term reliability. It was found that it does not affect. Note that the copper contained in the stainless steel reduces the contact resistance on the surface of the stainless steel.

These results revealed the following. That is, in order to increase the strength of the battery case 1, it is preferable to use stainless steel as the material of the battery case 1. Thereby, an internal short circuit becomes difficult to occur. In addition to this, by making the thickness of the battery case 1 0.2 mm or less, as the energy density is improved, the sealing property and the capacity retention rate are improved. As a result, the battery characteristics are improved and the long-term reliability is improved. Improved in safety and safety.

<Example 5>
SUS316L was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (thickness 0.1 mm) was 6 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Example 5.

<Example 6>
SUS316L was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (thickness 0.1 mm) was 10 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Example 6.

<Comparative Example 4>
SUS316L was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (thickness 0.1 mm) was 15 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 4.

<Comparative Example 5>
SUS316L was used as a material constituting the battery case 1, and the thickness of the battery case 1 was 0.2 mm and the outer diameter was 15 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 5.

<Comparative Example 6>
Iron (Fe) was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (thickness 0.1 mm) was 6 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 6.

<Comparative Example 7>
Iron (Fe) was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (thickness 0.1 mm) was 10 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 7.

<Comparative Example 8>
Iron (Fe) was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (thickness 0.1 mm) was 15 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 8.

<Comparative Example 9>
Iron (Fe) was used as a material constituting the battery case 1, and the thickness of the battery case 1 was 0.2 mm and the outer diameter was 15 mm. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Comparative Example 9.

The cylindrical batteries of Examples 1, 5, and 6 and the cylindrical batteries of Comparative Examples 2 and 4 to 9 were each manufactured in five pieces. For these cylindrical batteries, the occurrence rate of liquid leakage and the occurrence of internal short circuit The rate and the maintenance rate of the battery capacity were determined. These results are shown in Table 5. The internal short-circuit occurrence rate is a short-circuit occurrence rate when a tip of a round bar having a diameter of 1.0 mm is pressed against the side surface of the cylindrical battery and a stress of 1.5 kgf is applied in this state. The maintenance rate of the battery capacity was obtained after storing the cylindrical battery in an atmosphere of 85 ° C.-90% RH for 20 days. The battery capacity retention rate was determined based on the initial battery capacity.

By comparing Examples 1, 5, and 6 with Comparative Example 4 in Table 5, the material of the battery case 1 is the same SUS316L and the thickness is 0.10 mm. The difference was seen. That is, in Comparative Example 4 in which the outer diameter of the battery case 1 was 15 mm, an internal short circuit was likely to occur, whereas in Examples 1, 5, and 6 in which the outer diameter was 10 mm or less, an internal short circuit occurred. I did not. This is due to the following reason. That is, even when the battery case 1 is made of SUS316L having a high strength, when the outer diameter of the battery case 1 is large, the curvature of the side surface of the battery case 1 is reduced, and as a result, the external force is reduced. Thus, the battery case 1 is easily deformed. On the other hand, when the outer diameter of the battery case 1 is reduced, the curvature of the side surface of the battery case 1 is increased, and as a result, the battery case 1 is hardly deformed by an external force.

On the other hand, in Comparative Examples 2 and 6 to 8 where the material of the battery case 1 was iron (Fe), the occurrence rate of internal short circuit was remarkably high. This is because the strength of the battery case 1 is low, and therefore the battery case 1 is easily deformed by an external force. Further, in Comparative Examples 2 and 6 to 8, since the strength of the battery case 1 was low, liquid leakage was likely to occur. Further, in Comparative Examples 2 and 6 to 8, the capacity retention rate was remarkably low. This is because the battery case 1 is low in strength, so that the battery case 1 easily expands with the generation of hydrogen gas. Therefore, the sealing performance is lowered and the battery characteristics are deteriorated. In addition, it is thought that the battery case corroded due to the generation of hydrofluoric acid, which is a strong acid, and the corrosion caused the invasion of moisture and accelerated the progress of corrosion, so that it was impossible to maintain a high battery capacity. It is done.

These results revealed the following. That is, in order to increase the strength of the battery case 1, it is preferable to use stainless steel as the material of the battery case 1. Thereby, an internal short circuit becomes difficult to occur. In addition to this, by making the outer diameter of the battery case 1 10 mm or less, the sealing property and the capacity maintenance ratio are improved, and as a result, both the improvement of battery characteristics and the improvement of long-term reliability and safety are achieved. Is done. From the results of Comparative Examples 5 and 9, when the outer diameter of the battery case 1 is large (when it is larger than 10 mm), the long-term reliability can be obtained by increasing the thickness of the battery case 1 regardless of the material of the battery case 1. And safety are improved. However, when the outer diameter of the battery case 1 is small (when it is 10 mm or less), if the thickness of the battery case 1 is increased, the decrease in the internal volume becomes significant, and sealing by drawing becomes difficult. Sealability is reduced.

<Example 7>
As a material constituting the battery case 1, SUS316 (austenitic stainless steel having a carbon content of 0.08% by mass or less) was used. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Example 7.

<Comparative Example 10>
As a material constituting the battery case 1, SUS430 (ferritic stainless steel having a carbon content of 0.12% by mass or less) was used. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was designated as Comparative Example 10.

Example 5 Each of the cylindrical batteries of Examples 1 and 7 and the cylindrical battery of Comparative Example 10 were produced, and the liquid leakage occurrence rate and the battery capacity maintenance rate were determined for these cylindrical batteries. These results are shown in Table 6. The battery capacity retention rate was determined after storing the cylindrical battery in an atmosphere of 85 ° C.-90% RH for 20 days. The battery capacity retention rate was determined based on the initial battery capacity.

From the results shown in Table 6, it was found that in Examples 1 and 7 having a carbon content of 0.08% by mass or less, liquid leakage hardly occurred and the capacity retention rate was high. And more preferably, the carbon content was found to be 0.03% by mass or less.

Stainless steel with a low carbon content has a high elongation and a high tensile strength at break as shown in Table 1. Therefore, stainless steel with a low carbon content has high workability. That is, when forming the battery case 1, it is easy to stretch and thin the stainless steel, and the processing accuracy is high. Therefore, the battery case 1 having a small thickness can be formed easily and with high accuracy, and as a result, it is possible to stably manufacture a cylindrical battery having high sealing performance.

From this result, we found the following. That is, the stainless steel constituting the battery case is preferably a stainless steel having a carbon content of 0.08% by mass or less, particularly a stainless steel having a carbon content of 0.03% by mass or less. preferable. As a result, the sealing performance and the capacity retention rate are improved, and as a result, both improvement in battery characteristics and improvement in long-term reliability and safety are achieved.

<Example 8>
In Example 2, a cylindrical battery was manufactured under the condition that the negative electrode lead 6 was simply brought into contact with the battery case 1 without welding. Other manufacturing conditions are the same as those in Example 2. The cylindrical battery produced in this way was referred to as Example 8.

<Example 9>
In Example 1, a cylindrical battery was manufactured under the condition that the negative electrode lead 6 was simply brought into contact with the battery case 1 without welding. Other manufacturing conditions are the same as those in Example 1. The cylindrical battery produced in this way was referred to as Example 9.

For the cylindrical batteries of Examples 8 and 9, the internal resistance was determined. The results are shown in Table 7.

From the results shown in Table 7, when the negative electrode lead 6 is simply brought into contact with the battery case 1, the internal resistance is remarkably increased in Example 9 in which copper is not contained, whereas in Example 8 in which copper is contained. It was found that the internal resistance was significantly reduced. That is, it was found that the contact resistance on the surface of the stainless steel is reduced by mixing copper in the austenitic stainless steel.

This is due to the following reasons. That is, a protective layer that enhances acid corrosion resistance is usually formed on the surface of the stainless steel. When the stainless steel does not contain copper, this protective layer increases the contact resistance. On the other hand, when stainless steel contains copper, the resistance of the protective layer is reduced, and as a result, the contact resistance is reduced.

Therefore, welding of the battery case 1 and the negative electrode lead 6 can be omitted by mixing copper in the stainless steel constituting the battery case 1. Further, in the cylindrical battery in which the negative electrode lead 6 is welded to the battery case 1 (Example 2), for example, even when the welding is broken during use, the negative electrode lead 6 may be in contact with the battery case 1. In this case, a low internal resistance state is maintained.

Although the present invention has been described in terms of the presently preferred embodiments, such disclosure should not be construed as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains after reading the above disclosure. Accordingly, the appended claims are to be construed as encompassing all modifications and alterations without departing from the true spirit and scope of this invention.

The cylindrical battery according to the present invention can be used as a power source in various electronic devices such as portable digital devices.

DESCRIPTION OF SYMBOLS 1 Battery case 2 Negative electrode plate 3 Positive electrode plate 4 Separator 5 Electrode group 6 Negative electrode lead 7 Positive electrode lead 8 Sealing member 9 Gasket 10 Intermediate member 11 Disc

Claims

A cylindrical battery case with a bottom, an electrode group housed in the battery case together with an electrolyte, a sealing member fitted in an opening of the battery case, and a gasket interposed between the sealing member and the battery case And a cylindrical battery in which the opening of the battery case is sealed by drawing the opening end of the battery case,
The battery case is made of stainless steel,
The outer diameter of the battery case is 10 mm or less,
The thickness of the battery case is 0.05 mm or more and 0.2 mm or less,
Cylindrical battery.
The cylindrical battery according to claim 1, wherein the stainless steel constituting the battery case is austenitic stainless steel.
The cylindrical battery according to claim 1 or 2, wherein the stainless steel constituting the battery case is stainless steel having a carbon content of 0.08 mass% or less.
The cylinder according to any one of claims 1 to 3, wherein the stainless steel constituting the battery case is stainless steel having a copper content of 1.0 mass% to 6.0 mass%. Type battery.
The cylindrical battery according to any one of claims 1 to 4, wherein an outer diameter of the battery case is 6 mm or less.